Polystyrene relaxation behaviour

Watanabe H, Sakamoto T, Kotaka T (1985) Viscoelastic properties of binary blends of narrow molecular weight distribution polystyrene. 2. Macromolecules 18(5) 1008-1015 Watanabe H, Yao M-L, Osaki K (1996) Comparison of dialectric and viscoelastic relaxation behaviour of polyisoprene solutions Coherence in subchain motion. Macromolecules 29(1) 97—103... 

This chapter discusses the dynamic mechanical properties of polystyrene, styrene copolymers, rubber-modified polystyrene and rubber-modified styrene copolymers. In polystyrene, the experimental relaxation spectrum and its probable molecular origins are reviewed further the effects on the relaxations caused by polymer structure (e.g. tacticity, molecular weight, substituents and crosslinking) and additives (e.g. plasticizers, antioxidants, UV stabilizers, flame retardants and colorants) are assessed. The main relaxation behaviour of styrene copolymers is presented and some of the effects of random copolymerization on secondary mechanical relaxation processes are illustrated on styrene-co-acrylonitrile and styrene-co-methacrylic acid. Finally, in rubber-modified polystyrene and styrene copolymers, it is shown how dynamic mechanical spectroscopy can help in the characterization of rubber phase morphology through the analysis of its main relaxation loss peak. 

The molecular weight of a polymer influences its relaxation behaviour considerably. However, these effects can be modified considerably by the crystallinity of the material. Consequently it seems convenient to consider the influence of molecular weight under the separate headings of amorphous and crystalline polymers. Two representative examples will be discussed in some detail i.e. atactic polystyrene [25] which is a typical amorphous polymer and polyethylene oxide [33, 42 ] whose crystallinity varies with molecular weight, whilst brief illustrative references will be made to a number of other materials. 

Polystyrene exhibits relatively complex relaxation behaviour. Apart from the glass transition (a). 

Investigations of the electrophoretic behaviour of monodispersed carboxylated polystyrene latex dispersions as a function of particle size and electrolyte concentration by Shaw and Ottewill191 have confirmed, at least qualitatively, the existence of tea and relaxation effects. 

Figure 4 Master curve for the linear viscoelastic behaviour of entangd polymers in the terminal region of relaxation V Polystyrene, bulk (M=860000, T=190°C) Polyethylene, bulk (M=340000, T=130°C) A Polybutadiene solution (M=350000, <)) polymer=43%, T=20°C) [ om ref.4].

However, by making use of this definition, one has to conclude that many systems which look like a gel are in fact not covered by this definition aqueous poly(vinyl alcohol)/borate systems, which are known to show liquid-like behaviour at low frequencies [7], solutions of phase separated atactic polystyrene at temperatures above the glass transition temperature of the swollen polystyrene crosslinks, solutions of ABA block copolymers above the glass transition temperature of the swollen A-blocks, and even gelatin, which also shows creep behaviour, as shown by Ross-Murphy et al. [8,9] and by Kramer et al. (private communication), and a relaxation mechanism at extremely low frequencies, as is shown in Fig. 7 of the Section on gelatin, and possibly ako poly(vinyl chloride) in plasticizers [10-13]. The advantage of the approach of Kramer et al. [3] is that these systems certainly are covered by their practical definition. 

The relaxation with m = 0 approximates to the behaviour of polystyrene in solution. Once the value of n is greater than 5 the motions have become decoupled and the relaxation of the alkane block is almost independent of that of the styrene dimer. This implies that the size of the group in solution that is required for co-operative motion is approximately 5-6 carbon atoms. Similar analysis has been carried out on solid-state relaxations and it is generally found that the ot process involves motion of between 6 and 10 bonds depending on the polymer system. If we consider the co-operative motion of such an element it is possible to envisage that rotation about the backbone can occur without the... 

The measurements can be performed either on stretched samples below Tg or during stretching above Tg. As only the orientation behaviour of the labelled species is observed, it allows one to look at the molecular weight dependence of the chain relaxation processes of the labelled chain as well as the effect of the molecular weight of the matrix. Experiments carried out on polystyrene have clearly shown that the Doi-Edwards treatment of the shrinking of the chain in its tube has to be improved and a modified model has been proposed. 

The ultrasonic relaxation of an SBS triblock copolymer in dilute solution in toluene" corresponds to a superposition in appropriate proportions of the spectra of polystyrene and polybutadiene. The relaxation in the MHz frequency range is entirely predictable on the basis of the models described above except in one respect. The general relaxation spectrum in the MHz range is a composite of segmental and normal mode motions and the observed behaviour is calculated from... 

PET displays a rich variety of non-linear phenomena in its constitutive behaviour, and the endeavour of finding means to describe them mathematically is formidable. This is because beyond the common constitutive response exhibited by other amorphous polymers (e.g. polystyrene and polymethy methacryalate) such as yielding/stress softening and entanglement slippage, the behaviom of PET is further complicated by the evolution of a stress induced crystallisation and crystallisation enhanced stress relaxation process, where the details of the physical processes involved are still a topic of dispute. 

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